This proposal deals with chemically synthesized systems known as encapsulation complexes. They involve weakly bound assemblies in which a host structure completely surrounds one or more molecular guests. These systems are formed reversibly and exist on time scales of milliseconds to days, long enough for many types of interactions, and even reactions to take place within them. The encapsulated molecules are temporarily isolated and their behavior is effected accordingly: their motions and reactions are limited to the capsule, and they are protected from reagents inthe exterior solution or in other capsules. These features are relevant to molecular recognition, computational chemistry, low-barrier hydrogen bonds, autocatalysis and the rules governing molecular assembly. They have counterparts in biology: molecules-within-molecules resemble substrates surrounded by enzymes and agonists surrounded by receptors. They are all dynamic systems, largely shielded from solvent, in which motions are limited and interactions like hydrogen bonds may be magnified. The encapsulation complexes can also show nonlinear properties such as autocatalysis that are characteristic of living systems. The encapsulation of peptides and nucleic acid derivatives takes a step toward the use of these systems for drug delivery. We intend to study how the capsules recognize their guests, how the guest molecules get into and out of the capsules, the nature of the space inside the capsules, their transport properties. We also propose to synthesize new and larger capsules, especially those made up of many identical molecular subunits.